Allen-Bradley LOGIX 5000

Process Control Instructions
Chapter 1
Rockwell Automation Publication 1756-RM006K-EN-P - November 2018 55
Execution
Function Block
Condition/State Action Taken
Prescan EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is false EnableIn and EnableOut bits are cleared to false.
Tag.EnableIn is true EnableIn and EnableOut bits are set to true.
The instruction executes.
Instruction first run N/A
Instruction first scan N/A
The instruction does not execute, but does validate input
parameters.
Postscan EnableIn and EnableOut bits are cleared to false.
Structured Text
Condition/State Action Taken
Prescan See Prescan in the Function Block table.
Normal Execution See Tag.EnableIn is true in the Function Block table.
Postscan See Postscan in the Function Block table.
Example
In this example, the DEDT instruction simulates a deadtime delay in a simulated
process. The output of the PIDE instruction is passed through a deadtime delay
and a first-order lag to simulate the process. The array DEDT_01array is a REAL
array with 100 elements to support a deadtime of up to 100 samples. For example,
if this routine executes every 100 msec, the array would support a deadtime of up
to 10 seconds.